The announcement came on a weekend, just as the world’s attention was diverted by tense negotiations toward an Iranian nuclear deal. On Saturday, Nov. 23, Beijing announced “aircraft-identification rules” for an “East China Sea air-defense identification zone” that includes the skies over a scattering of rocks that China calls the Diaoyu.

Japan, which currently administers the outcroppings and uses the name Senkaku to refer to the contested territory, has cried foul. On Sunday, Japanese Foreign Minister Fumio Kishida said that Tokyo refused to recognize Beijing’s division of the heavens. “It was a one-sided action and cannot be allowed,” Kishida said, warning that Beijing’s move was “expected to trigger unpredictable events.”

The rules mean that Beijing now requires aircraft flying through this patch of sky to report their flight plans to Chinese authorities, remain in radio contact with them and make their nationalities and logos clear. “China’s armed forces will adopt defensive emergency measures to respond to aircraft that do not cooperate in the identification or refuse to follow the instructions,” reported Xinhua, the official Chinese news agency.

Wars have been triggered by far less than the uncertain custody of a few remote specks of land. For more than a year now, tensions have simmered over the contested five islets, with patriotic rhetoric emanating from both sides after Japan nationalized three of the outcroppings in September 2012. The Japanese government says it bought the tiny territories from their private owners for fear they would be purchased by Tokyo’s jingoistic then governor.

Military posturing has surged too. This year, Japan unveiled its largest warship since World War II, while China’s military budgeting continues to escalate. Japan has repeatedly scrambled its jets to counter what it considers potential Chinese threats, including the first reported unmanned Chinese drone to fly near the Diaoyu/Senkaku islands. (The drone did not violate what Japan considers its airspace.) China has also increased the number of its vessels sailing the resource-rich waters surrounding the disputed islands.

To complicate matters, Taiwan, which calls itself the Republic of China (ROC), claims ownership over the bits of East China Sea rock as well. Its government said on Sunday that the disputed islets “are an integral part of ROC territory, a fact which is unaffected by mainland China’s declaration.” China’s newly announced air-defense identification zone (ADIZ) also overlaps with one that had been previously set out by South Korea, leading Seoul to describe the Chinese parameters as “regretful.” (Each nation is free to carve out its own ADIZ, which can extend beyond a country’s own airspace, setting up the potential for competing zones.)

Still, most concerning is the geopolitical discord between the world’s second largest and third largest economies. The current enmity comes as China, under the leadership of President Xi Jinping, has been more actively pursuing territorial interests in another waterway, the South China Sea, straining Beijing’s relations with Vietnam and the Philippines, among other Southeast Asian nations. China has beefed up administrative controls over these South China Sea shoals, reefs and islets, even going so far as to promote Chinese tourism and business opportunities in some of the contested territory. Southeast Asian nations have responded by cozying up to the U.S. and even, on occasion, Japan.

Over the weekend, the U.S., which is bound by a security treaty to defend Japan should it come under attack, waded into the ADIZ controversy. “The United States is deeply concerned by the People’s Republic of China announcement today that it is establishing an air defense identification zone in the East China Sea,” said a statement from U.S. Secretary of Defense Chuck Hagel. “We view this development as a destabilizing attempt to alter the status quo in the region. This unilateral action increases the risk of misunderstanding and miscalculations.” Although the U.S. claims it does not take sides on who rightfully owns the Diaoyu/Senkaku, Washington has repeatedly said that the American alliance with Japan covers the islets. Hagel’s weekend statement reiterated that “the U.S.-Japan Mutual Defense Treaty applies to the Senkaku Islands.”

On Monday, Japan’s hawkish Prime Minister Shinzo Abe told the Japanese legislature that the creation of a Chinese air-defense identification zone was “a profoundly dangerous act that may cause unintended consequences.” Characterizing China almost as some rogue actor in international politics, he added: “Japan will ask China to restrain itself while we continue cooperating with the international community.”

In turn, China has expressed dissatisfaction with Japan’s criticism of the newly formed ADIZ. A spokesman for the Chinese Ministry of National Defense labeled Japanese concerns “utterly groundless and China won’t accept them,” explaining that the creation of the ADIZ was “totally rational and indisputable.” China has lodged formal complaints, or what Chinese state media called “solemn representations,” with both the Japanese and U.S. embassies in Beijing.

Early next month, Chinese officials will have the opportunity to discuss the American position on the territorial dispute in person with U.S. Vice President Joe Biden, who is scheduled for an Asian tour. Unsurprisingly, he will also be visiting Japan.